The present invention relates generally to a downhole mechanical anchor setting system which can be positively set in variable positions.
A perforating gun is commonly used in downhole systems for perforating hydrocarbon formations for producing wells. As is well known, selective perforation allows either oil or gas to flow to the present production zone depending on the type of well.
The prior art teaches various types of perforating gun systems and methods of operation, each having different functionality. For example, past systems disclose a perforating gun string that allows several perforating discharges to be set without having to reload. Such a system allows the perforating gun to create perforations at different depths in the same well bore without uphole retrieval after each discharge.
One problem with the use of a perforating gun is that it typically recoils when it is discharged. The recoil can cause the perforating gun assembly to surge upward within the well which can cause significant damage to the perforating gun and wireline or coiled tubing equipment. Further, if the perforating gun operates effectively then oil and gas may also surge uphole which can similarly cause equipment damage.
Partial solutions to the perforating gun""s recoil problem have been provided in different forms of mechanical anchors. For example, these mechanical anchors may arrest the movement of the perforating gun when it is discharged and/or use slips or grips which frictionally engage the casing or formation at an increasing rate as increasing upward pressure is applied.
An example of a expanded slip well anchor is taught in U.S. Pat. No. 5,348,090. This anchor teaches a body and a mandrel that is longitudinally movable through the body. Attached to the mandrel are two sets of slips which are designed with opposing wedged surfaces to engage each other. When the slips are engaged they expand outwards and frictionally engage the casing or formation. This patent teaches setting the position of the anchor by using shearing pins. However, this patent does not teach an apparatus or process to reset the anchor""s position.
Another anchor is taught in U.S. Pat. No. 6,152,233 issued on Nov. 28, 2000. This patent teaches an anchoring system which can be repeatedly positioned at different locations within the well without removing the system from the well. However, this patent does not teach an apparatus having more than two internal setting positions, including a setting where the anchoring system is set (engaged), a setting where the anchoring system is not set allowing downhole movement (disengaged) and a setting where the system is not set allowing uphole movement (intermediate).
More specifically, the prior art does not teach selective internal setting positions. This means that in certain past devices, tension must be applied to hold the slips in an engaged (or set) position and a sinker bar or reliance on gravity is used to release the slips from their engaged position. Further, without an intermediate setting position, in the past, the entire tool assembly cannot be positioned uphole without applying the appropriate amount of upward tension of the wireline (without engaging the slips) to move the mandrel at the same time as the sleeve. Accordingly, there has been a need for a mechanical anchor setting system having multiple and selective setting positions allowing uphole and downhole movement and positive setting and release of mechanical anchors.
The present invention teaches an apparatus and process for positively setting the mechanical anchor in at least three positions. At a minimum, the mechanical anchor setting control system provides a set position where the slips are engaged, another position where the slips are not engaged and an intermediate position between the engaged and disengaged positions which allows easy movement of the mechanical anchor assembly uphole.
The mechanical anchor setting system comprises a mandrel longitudinally moveable through a sleeve, a slip system operatively connected to the sleeve and the mandrel (for gripping the casing or formation when the slips are engaged) and a setting control system operatively connected to the sleeve and the mandrel.